got a S&W 2x3 chassis roadster 105 inch WB car will not go straight. has a LS motor 650 ish HP
launch ok but goes out and its turning the tires on the shift noticed whiling looking at a few pictures on the launch its twisted up pretty good LF is a few inches in the air this car does not have a anti roll bar. 4 link is pretty wide at 25 and it has a 95lbs spring on the RR and a 80lbs on the LR. anyone rec a good starting point on the IC before the motor swap it was perfect the owners is telling me old motor was about 400 HP ish he said. I have not measured anything yet on this someone else has had there hands on it and scaled it but has not made any 4 link changes the corner weights are with in 20 lbs I can post them if needed
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Do you have a video of the car launching?

77,

For several years now I have added an anti-roll bar on "everything" They work and help and I find no downside to adding one.

About the rear springs, I have not found any reason to install unequal rates, a set of 95 pounds springs will most likely be just right. It is OK to raise the spring seat as much as 1/3 of the available threads to attain the ride height wanted. [but not necessary, if the ride height is good with spring seat at the bottom that is also OK.]

With the anti-roll bar added, disconnect the right side link. Then, the right upper four-link bar can be turned one flat short from neutral. After that, install the right side anti-roll link and just take the slack out making it longer.

Also, be sure to check the entire car's suspension for any loose or worn parts, binding rod ends, weak shocks, and pay attention to front end setup and alignment.

One more thought, if you plot the four-link, 55" out and 5 1/2 off the ground will be close.

I would scale the car and find out where the IC is on it.
I agree with putting a good stiff anti-roll bar on it.
Seems like you have everything all messed up, find out what you got. Video of launch could help to see what it is doing. Once you find out what you have as far as settings and what it is doing then we can make adjustments from there.
I would also check to make sure rear end is straight and then jack up car and remove rear shocks. move rear end through complete cycle to see if there is anything binding or moving.

When I first installed my 4-link, I never had an anti roll bar. Every time I launched, it felt like I was going to change lanes.

Installed an anti roll bar. Front end now lifts straight up with no twist enough that I barely need to hold the steering wheel.

As a rough guess, I'd say to put the IC about a third of the way ahead of the axle and right on the neutral line for a start. If it picks up the front end, lower the IC.

You need anti roll bar installed before even trying to get it sorted out. Spend the money and save yourself tons of grief.

Here are my corner weights when I had a 60lb bar hanging centered as far back as possible. 1.22-1.25 60' high 5.60s to low 5.70s. Goes straight and true now that I got the rear squared where it needed to be. Nave never had a problem at the shift. I do not have an anti-roll bar.

quote:

Originally posted by racerdude2054:
Do you have a video of the car launching?

I do not the customer brought me a picture. I done not do chassis work for a living but I have built many cars and done some fab work so he asked me to see if I could get this car figured out.

quote:

Originally posted by Curly1:
I would scale the car and find out where the IC is on it.
I agree with putting a good stiff anti-roll bar on it.
Seems like you have everything all messed up, find out what you got. Video of launch could help to see what it is doing. Once you find out what you have as far as settings and what it is doing then we can make adjustments from there.
I would also check to make sure rear end is straight and then jack up car and remove rear shocks. move rear end through complete cycle to see if there is anything binding or moving.

I am going to start from scratch with this since a few people have worked on this already plan to do some measuring this week. I will install the anti roll bar also. def going to swap out the rear springs to a new matched pair also. going to check front end alignment also. I believe back in the day when this car was new it had a BBC and ran low 8's with no problems but a lot im sure has changed since it was originally built

And we all want to help you but with out knowing corner weights and IC and no video to tell for sure what it is doing it is all just a wild guess.

curly I will get the weights and the 4 link measurements. I plan to start working on this tomorrow night

On my altered with the 4 link it liked about 60 Lbs more on right rear if I remember right.
Now that is with a good anti-roll bar. Also one of the things I do was put about half of that preload in with the upper right 4 link bar and then the rest I would raise up right rear spring.

In my opinion for what that is worth I do not like to put all of the preload in with the bar because I think it puts a binding situation in it. I think it was around 4 flats on the bar and about half inch up on the spring to get it where it went nice and straight even with wheels in the air.

What I did was scale the car. Set it up neutral and then made one flat change at a time and marked down the difference. I think it was around 25 Lbs change for each flat of preload.
Then I went out to the track. I took off rear body panels, looked like (well you know) raised wheelie bars up pretty high and made some passes. First pass it went to the right. Added more and more preload until it was going straight. Ended up with like 6 flats and I felt that was too much for my car. (It has very short bars so it is different than most all others out there) But it was going nice and straight. So I then moved it back to like 4 flats and added some with right rear spring. You must have anti roll bar unhooked while adjusting preload and then set that anti roll bar neutral if you make any 4 link adjustments.
I made a chart and painted one of the flats at neutral. With that system I could tell you pretty close what my corner weights were with out putting it on the scales.
After you get it going straight if you can scale it again then you will have a good baseline to go back to any time. If it takes too much preload to make it go straight then you will have other problem with it wanting to move around when you hit the brakes. Do not preload more than you have to

Once you get it there the wheelie bars also become a tuning tool if it is carrying tires out there.

All of this is ASSUMING you have the IC close to where it needs to be. On my early settings it was pulling the wheels way up and hitting bars way too hard. Moved top bar down and changed IC a little and then it was pulling front wheels a foot or so and carry them way out there. But it was gentle and smooth with 100% on rear wheels and wheelie bars were just fine tune.

So your IC determines how hard it hits rear tires and how it tries to lift front end and push car forward. Preload helps it go straight under power and is really critical if you are carrying front tires out there.

When you say it is not going straight but you did not say what direction it is going.

It all comes down to find out what you have for a baseline, what it is doing then making changes to move it in right direction until it is right.

did some measuring
weights are
LF 460
LR 521
RF 464
RR 510
this is with driver


4 link measurements I came up with are 41.5 and 7 up not 100% this is correct measurements below
lower bar 8 1/4 off the ground in the front
lower bar in the rear is 9 inches from ground
upper bar in front is 14.5 from ground
upper bar in rear is 19 1/4 from ground
upper bar length is 15.5
lower bar length is 16
bars are mounted ****hest away from the axle tubes
crank centerline is 11 inches
rear tire is a MT 31X13X15 PN 6218

quote:

Originally posted by camaro77:
did some measuring
weights are
LF 460
LR 521
RF 464
RR 510
this is with driver

Your mileage may vary but I will tell you on my car if it was like yours it would not make it down the track. Mine likes about 60 Lbs MORE on right Rear.
Let me guess your car is making a hard right at the hit?

I had another good talk with the owner and he says it feels like it just wants to spin the tires on the 1-2 shift which is about 330 mark area and it wants to have the car make a sudden turn im thinking this could be caused by the short IC I did order a antiroll bar for it tonight going to install that and see if I cant get the IC further out the rear suspension brackets are very limited with adjustability from S&W racecars

You still haven’t said which Direction it wants to turn at the shift? Would think it would go right at the hit with those corner weights. Did you measure all 4 bar lengths and rear end alignment?

What suspension is on the front?

The IC determines how hard it hits the tires, how much lift it applies to the front and where it pushes car forward.

The preload (through bar settings and or spring) determines what direction it goes. That is assuming you have good rod ends and everything is straight and square.

Shorter IC will try to lift back of car more, longer lifts front more.

How high the IC is also makes a difference.

We are still back to square one. We do not know exactly what car is doing so no way we can give you any direction on how to fix it.

Not hooking up or hard wheelies look at IC. Not driving straight look at chassis square or corner weights.

Just by looking at those corner weights I can assume it is trying to go to the right. I know mine would hang a hard right and look for a guard rail or Christmas tree.